FIG. 5 is a sectional view showing a conventional motor-vehicle-destined AC dynamo machine provided with a rotational position detector for the control purpose (hereinafter also referred to as the control-dedicated rotational position detector only for the convenience of description). This AC dynamo machine is equipped with a pulley 60 at a right-hand end portion, as viewed in FIG. 5, for making it possible to transmit bidirectionally a motive power with an engine. The pulley 60 is fixedly secured to a rotatable shaft 12 at one end portion thereof by means of a nut 61.
Mounted fixedly on the rotatable shaft 12 is a rotor core 8 which is wound with a field winding 9. The rotor core 8, the field winding 9 and the rotatable shaft 12 cooperate to constitute a rotor 10. Disposed in opposition to the rotor 10 is a stator core 1 which is wound with a polyphase stator winding 2. The stator core 1 and the polyphase stator winding 2 cooperate to constitute a stator 3.
The rotor 10 and the stator 3 are housed within a bracket 80. The rotor 10 is rotatably supported by a pair of bearings 16 and 17. The bearings 16 and 17 and the stator 3 are stationarily disposed internally of a bracket 80. Slip rings 15 are mounted on the rotatable shaft 12 on one side for the purpose of current supply to the field winding 9. A pair of brushes 13 are provided to slideably contact the slip rings 15, respectively. Further, a brush holder is provided in which springs 14 are accommodated for pressing the brushes 13 against the slip rings 15, respectively.
Furthermore, a resolver 20 designed to serve as the control-dedicated rotational position detector is disposed on the rear side of the AC dynamo machine oppositely to the pulley 60. The resolver 20 is comprised of a rotor 21 and a stator 22. The rotor 21 is secured to the rotatable shaft 12 at an end portion 12a thereof. The stator 22 is provided with a stator winding 22a. 
The resolver 20 is secured to a resolver bracket 80a by means of a retainer 24 and a screw 23 which fix the stator 22 in the axial direction. The retainer 24 is formed in an annular shape and clamped to the resolver bracket 80a by the screw 23. A cover 25 is externally provided for the resolver 20 in order to protect the resolver against invasion of foreign materials from the exterior.
Next, description will be made of operation. When an exciting current is fed to the field winding 9 through the medium of the brushes 13 and the slip rings 15, magnetic flux is generated in the rotor core 8. In a motor operation mode for starting the engine operation, a polyphase alternating current is fed to the polyphase stator winding 2 in the state mentioned above, as a result of which a turning force or torque is generated in the rotor 10 to be transmitted to the engine by way of the pulley 60 and a belt, whereby the engine is driven. At this juncture, it should be mentioned that although the pulley 60 and a poly-V belt are employed as the turning force transmitting means in the case of the instant example, a toothed belt or chain or the like may be used as the belt.
On the other hand, in the generator operation mode for supplying an electric power to vehicle-onboard electric loads, the exciting current is fed to the field winding 9 through the medium of the brushes 13 and the slip rings 15, which results in generation of the magnetic flux in the core 8. In this state, a turning force is transmitted to the rotor from the engine through the belt via the pulley 60, whereby the rotor is forced to rotate. Thus, an electric power is induced in the polyphase stator winding 2 under the action of the rotating rotor.
In the motor-vehicle-destined AC dynamo machine of the structure described above, electrical energization of the exciting winding of the stator 22 of the resolver 20 in the state in which the rotor 21 of the resolver 20 is rotating will result in generation of two-phase output voltages in the winding of the stator 22 which voltages change in conformance with a sine curve and a cosine curve, respectively. Through comparison of both voltages, the rotation angle (absolute position) can arithmetically be determined.
In the conventional motor-vehicle-destined AC dynamo machine implemented in the structure described above, the resolver 20 serving as the control-dedicated rotational position detector is so designed as to arithmetically determine the rotation angle on the basis of the voltages induced in the stator winding 22a wound around the stator 22. Consequently, when leakage flux from the AC dynamo machine 100 crosses or interlinks the stator winding 22a, it becomes impossible to detect the rotation angle with reasonable accuracy, giving rise to a problem.
The present invention has been made with a view to solving the problem mentioned above, and thus an object of the present invention is to provide a motor-vehicle-destined AC dynamo machine which is capable of detecting the rotation angle with high accuracy by reducing noise generated in the control-dedicated rotational position detector.